This invention relates to a method and apparatus for the in-line repair or replacement of pipelines, and more particularly to a novel and improved method and apparatus for the in situ repair or replacement of natural gas pipelines.
Numerous methods have been devised for the repair or replacement of gas pipelines. One method requires a trench to be excavated from a stop valve located upstream from the section of pipeline to be replaced. Manipulating the valve then stops the gas flow and the pipeline section is replaced. This method was improved by the development of devices that temporarily block the flow of gas in a pipeline. This method did not require the excavation of a stop valve but functioned by inserting into the pipeline a device that could be expanded and thereby block the flow of gas in a pipeline. Both of these methods were very time-consuming and labor-intensive. Another method allows the gas to escape to the atmosphere while the pipeline is replaced. However because of the long term and continuous exposure to gas, this method required the use of special equipment such as fire resistant clothing and respirators for the workers. Additionally, the released gas constitutes a safety hazard.
Devices for temporarily stopping the flow of gas in a pipeline are shown in U.S. Pat. Nos. 5,590,676 and 4,127,141. The '676 patent discloses a stopper for an opening in a gas pipeline side wall having an expansion plug that can be axially compressed, thereby expanding the plug to fill and seal the pipe. The '141 patent teaches a method and apparatus for sealing an opening in the side wall of a pipeline that includes a plug wrench having an elongated stem and a stopper rod that can be moved relative to a threaded jack member to cause a resilient plug to radially expand.
Tools for temporarily stopping the flow of gas in a pipeline are shown in U.S. Pat. Nos. 5,592,965; 4,597,147 and 5,819,804. The '965 patent discloses a valve stop changer including a tool having a tubular expandable plug member which is compressed and expanded by rotating a handle to move into sealed engagement with a pipe. The '147 patent discloses a changer tool for use in removing a valve under pressure. The tool is a shaft supporting a compressible rubber plug that is inserted through the valve into the upstream pipe. The plug is then compressed into sealed engagement with the inner wall of the pipe. The '804 patent is directed to a specific improvement in an expansion tool for a pipeline.